Smbolic integration error with piecewise function of two variables.

Consider the following toy problem in MuPAD:

assume(x in R_): assume(y in R_):
px := piecewise([x>5,a],[x<=5,b]):
py := piecewise([y>7,c],[y<=7,d]):
pxpy := px*py

The function pxpy is accurately computed. However, the following line gives undefined:

pxx := int(pxpy,y=-10..10)

whereas the answer should be

3*a*c + 17*a*d if x>5 
3*b*c + 17*b*d if x<=5

Also, the following works, but I don't want to do this manually.

pxx1 := int(pxy,y=-10..10) assuming x>5
pxx2 := int(pxy,y=-10..10) assuming x<=5
pxx := piecewise([x>5,pxx1],[x<=5,pxx2])

How can I solve this problem? Is this a bug?